An amicus curiae (also amicus curiæ; plural amici curiae, literally "friend of the court") is someone who is not a party to a case, who offers information that bears on the case but who has not been solicited by any of the parties to assist a court. This may take the form of legal opinion, testimony or learned treatise (the amicus brief) and is a way to introduce concerns ensuring that the possibly broad legal effects of a court decision will not depend solely on the parties directly involved in the case. The decision on whether to admit the information lies at the discretion of the court. The phrase amicus curiae is legal Latin.

Noun1. an adviser to the court on some matter of law who is not a party to the case; usually someone who wants to influence the outcome of a lawsuit involving matters of wide public interest (synonym) friend of the court (hypernym) adviser, advisor, consultant (classification) law, jurisprudence